The invention relates to a device for detecting the location of an edge of a transparent, anisotropic material, comprising at least one sensor with a light source, two polarization filters with transmission axes meeting at a 90xc2x0 angle as well as a light detector, whereby the light source and one of the polarization filters are located on the edge to be detected and the second polarization filter and the light detector are located on the other side.
The invention further relates to a web edge control with such a device, a control device and a web edge adjustment device as well as a printing press with such a web edge control.
A device for detecting the location of the edge of a transparent material is known from U.S. Pat. No. 5,751,443, whereby such light is to be directed on the transparent material so that it is reflected and then the reflected light is detected, in order to determine the location of an edge. The problem with a sensor using this method is that, if the material is soiled, the reflection properties are weakened, and thus the detection of the location of the edge is inaccurate or impossible. This is particularly true of continuous webs that transport goods, as well as printing presses, particularly electrophotographic printing presses that are equipped with a transparent web to convey printing substrates. Such web edges must, however, be detected, in order to adjust the location of the web.
A device from DE 199 06 154.8 of the type mentioned at the beginning was suggested to solve this problem. Its operating principle is based on the fact that polarization filters with transmission axes meeting at a 90xc2x0 angle allow no penetration of light, since such polarized light passes only through the first polarization filter, which is blocked by the second polarization filter. If an anisotropic material with an excellent optical axis is introduced between the polarization filters, a beam or partial bean may occur, whose polarization direction is turned to 90xc2x0. This light penetrates the second polarization filter, so that a clear image of the material edge is produced on the light detector. This image is basically much more resistant to soiling than the image based on a reflection. However, the problem with this suggestion is that a beam or partial beam with a turned polarization direction does not occur if the light along the optical axis of the transparent material enters into this material. The light must then form an angle to the optical axis, which ensures that there is an easily detectable amount of light that is turned in its polarization direction. However, due to the manufacturing procedure and stress, the optical axis of transparent, anisotropic materials also has different alignments with a material of the same chemical composition. Such a device must thus be aligned with the respective optical axis in which the beam is turned in its polarization direction with an easily detectable intensity. Due to the above-mentioned reasons, this alignment must, however, be repeated with each piece of material to be detected. Where a wet to convey a product is concerned, each change of the web to a new web requires an alignment of the sensor with the optical axis of the new web. This problem may also well occur with an increase or decrease of the stress of the web.
In contrast to this suggestion, the task of the invention is to configure a device for detecting the location of an edge of a transparent, anisotropic material that does not require assembly for the detection of material with optical axes in various directions.
This task can be achieved by having at least one sensor of this type that can be arranged and/or is configured, so that various angles between the transmission axis of the first polarization filter and the optical axis of the transparent, anisotropic material are possible.
Thus a device would be provided that can detect the edge of a transparent, anisotropic material and whereby, by means of a simple tilting motion or another change of position with change in the angle direction of the polarized light, a position can be achieved in which the alignment to the optical axis of the respective material required to detect the material is possible. In this manner, it is possible to obtain the exact location of this type of material edge, which is relatively resistant to soiling and which thus solves the problem stated at the beginning, particularly where continuous web edge controls and webs transporting material, such as the web edge control for transparent, anisotropic webs of electrographic printing presses, are concerned.
The problem of the different optical axes occurs primarily because the optical axes of webs have various directions as a result of the manufacturing process and that the detection and adjustment of the location of such a web is difficult. The device according to the invention provides a web edge control in which the optical path is directed or can be directed to the edge of a transparent, anisotropic web to be detected in such a way that all possible courses of optical axes as a result of the change of the optical axes of the/a web can be adjusted, without requiring assembly. To this end, a sensor can be arranged such that it can be tilted, and several sensors can be arranged at various angle positions and the corresponding sensor can be selected or the optical path of one sensor of this type can be configured so that it is adjustable, and thus it and the polarized light can take various angle positions to the material to be detected and thus to its optical axis.
Particularly in the case of printing presses, the device according to the invention can reduce the maintenance costs, the use of assembly staff, and the machine downtime during a change of the web. Also with a change in the stress of a web and a concordant change of the location of the optical axis, the device can be aligned with the direction of the optical path without great expense. Another use for the invention is the detection of the edge of individual piece of material, since in this case as well, the different course of the optical axes must be taken into account.
The device according to the invention provides a simple means such that the polarized light takes an angle position to the material, in which a turn of the light emitted from the first polarization filter passes through the material to be detected to a sufficient degree to detect an edge, whereby an angle between the transmission axis of the first polarization filter and the optical axis of the transparent, anisotropic material is preferably selected, in which the best possible image of the edge on the light detector can be achieved. An optimum is achieved with a 45xc2x0 angle, although an angle within the range of 25xc2x0 and 65xc2x0 will suffice to show an image of an edge.
There are various ways to configure the placement of the sensor in various positions to achieve the above-mentioned angle or another alignment of various angle positions of the polarized light to the material to be detected. It can be set up so that the angle between the transmission axis and the optical axis is exactly positioned or so that an angle position of a sensor is selected that lies in the 25xc2x0 to 65xc2x0 angle range. It is often sufficient to use two defined angle positions and that the angle position to the respective material is selected in which the edge is better shown. However, a plurality of multiple defined angle positions can also be envisaged, whereby the angle position to the respective material is selected in which the edge is better shown. The latter or an exact positioning of the angle is useful if the directions of the optical axes of the material to be detected is not limited to a particular angle range, but the optical axes can take all the various directions possible or, if a good image of the edge requires that the most optimal angle be selected, that the best optimal angle is selected, such as when a material of reduced transparency, caused by soiling, for example, is to be detected.
The sensor may also be tilted manually into the various positions and locked in this position. This can be implemented with any simple mechanics. A drive may also be used, which places a sensor in the most optimal position of possible positions with various angle positions. This is an advantage if the sensor is mounted on a part of the machine that is difficult to reach. In addition, a control can be used that is connected with the light detector and that the angle position for the image of the edge is selected on the light detector. This can, for example, permit the placing of a sensor in its optimal position. For example, the control can ensure that several positions are switched through and that the most contrasting image of the edge is selected. But it can also select the most optimal optical path from angle positions of several optical paths installed in any manner, or adjust an optical path in a corresponding manner. This type of device is very comfortable, since no further operating effort is required. If the material to be detected concerns individually transporter pieces that have optical axes in various directions, then this type of control is a very useful solution, since it automatically ensures very good detection of the edges.
In addition, a control can be further configured so that it adjusts the intensity of the light source and/or the responsivity of the light detector. The advantage of this control is that the device reacts automatically to a change of conditions and thus ensures a flawless image of the edge. Such changes may be due to some contamination, or because materials of various intensities of transparency are to be detected.
The control can adjust the set points on the basis of a corresponding algorithm of a program, or it is possible that the control has programmed set points for defined positions. In this manner, an optimal positioning is ensured.
The light detector may comprise several optical receiving components: for example, it may be configured as rows of optical receiving components, e.g., forming a CCD row, or it is possible that the light detector is configured as a flat receiver. With such arrangements, digital set points for further processing in an electronic control have been produced. In this sense, a flat receiver has the advantage that, by means of a single receiver, the inclined position of an edge can be detected.